AudioServicesAddSystemSoundCompletion: how to use the void* parameter?

Question

Hello, guys.

I want to play two sounds, but the last one only after the first ends.

I'm using AudioServicesAddSystemSoundCompletion like that:

  NSArray  *data      = [NSArray arrayWithObjects:target, callback, nil]; 
  NSString *soundPath = [bundle pathForResource:sound ofType:type];

  SystemSoundID soundID;
  AudioServicesCreateSystemSoundID((CFURLRef)[NSURL fileURLWithPath: soundPath], &soundID);
  AudioServicesAddSystemSoundCompletion(soundID, NULL, NULL, playSoundFinished, data);

  AudioServicesPlaySystemSound(soundID);

and my playSoundFinished method:

static void playSoundFinished(SystemSoundID soundID, void *data) {

    NSArray *data_ = (NSArray *)data;
 id  obj    = [data_ objectAtIndex:0];
 SEL method = NSSelectorFromString([data_ objectAtIndex:1]);

 [obj performSelector:method];

}

The documentation stats that the last parameter must be a void* and that it's the data to work in callback method, but how can I use the NSArray that I pass as argument? I'm new in C and Objective-C, so sorry if it's a dumb question. Casting works fine, but when I try to access the first position, a bad execution occurs. I really didn't understand why void* type. What that means?

In this other post the guy pass a UIButton without any casting and that idea didn't work for me too.

Can you help me?

Thanks in advance.

Answer 1

You need to retain your NSArray somewhere before passing it to your completion routine as a void*. The OS can't do it because it doesn't even know if a void* is an object or not.